Thermal kinetics of color degradation of mulberry fruit extract

The effects of temperature and pH on color degradation kinetics of the mulberry fruit extract were investigated. The absorbance at 5 10 mn was decreased with increase of heating time, but that at 420 nm was increased with the increase of heating time at 100degreesC. The change of the browning index (A(510)/A(420)) was increased with increase of pH and was lower at pH 2.0 than that at pH 5.0. The browning index variation was adequately described by both the first-order and the zero-order kinetic. However, the zero-order kinetic model was proposed because of the better fit. According to the Arrhenius model, the activation energies for the browning index in the range of 80-100degreesC for the four different pH values were 30.68 kJ/mol for pH 2.0,35.87 kJ/mol for pH 3.0,42.67 kJ/ mol for pH 4.0, and 43.49 kJ/mol for pH 5.0.